Reverse battery protection circuit

Abstract: A protection circuit (10) for protecting internal circuitry of an integrated circuit (26) from a reverse battery connection has been provided. The protection circuit includes a pass transistor (14) which is rendered operative when the supply voltage is properly connected to the integrated circuit. However, when the power supply is improperly connected, a second transistor (32) becomes active thereby rendering the pass transistor inactive and not allowing the reverse supply voltage to be applied to the internal circuitry.

Description: Field of the Invention This invention relates to protection circuits and, in particular but not limited to, a reverse battery protection circuit for use in automotive applications. Background of the Invention There currently exists numerous types of electronic integrated circuits (IC's) for use in the automotive industry. Generally, the power supply for these circuits is generated from a 12-volt battery in an automobile. However, automotive IC's tied to the battery must survive the battery being hooked up backwards, for example, to avoid forward biasing epitaxial layers of the IC that are tied to the battery which thereby could result in destruction of the IC. One attempt that prior art has made for providing reverse battery protection for IC's is to include a series diode between the battery and the integrated circuit wherein if the integrated circuit is connected to the battery backwards, the series diode is reversed biased and prevents supply voltage from being applied to the integrated circuit. However, the series diode solution compromises low voltage performance and the geometry of the diode becomes larger as supply current requirements increase. Another attempt that prior art has made in providing reverse battery protection for an integrated circuit is to provide a saturated lateral PNP transistor in series between the battery and the integrated circuit. Although low voltage performance is not compromised in this solution, base current requirements for the lateral PNP increase power dissipation and the geometry of the PNP transistor becomes large as supply current requirements increase. Another attempt that prior art has made in providing reverse battery protection for an integrated circuit is to provide a charged pumped reverse TMOS transistor as a pass device between the battery and the integrated circuit wherein the TMOS transistor has passive (resistive) gate to source termination. However, this solution requires DC current from the charge pump to enhance the TMOS transistor, and the turn off time of the TMOS transistor is limited by the size of the passive gate termination. Moreover, the charge pump must be high impedance when the supply voltage is reversed. European patent applications nos. EP-A-0349836 and EP-A-0626745 and German patent application no. DE-A-3930091 give examples of reverse battery protection circuits. European patent application no. EP-A-0626745 is however only prior art for this application under Article 54(3) EPC as regards the set of claims for Germany and does not disclose biasing an epitaxial region containing elements of the reverse battery protection circuit. Hence, there exists a need for an improved reverse battery protection circuit for an integrated circuit that does not compromise low voltage performance, can efficiently handle moderate supply currents, does not demand DC current from a charge pump, and has a fast turn off time. Summary of the Invention The subject matter to be protected for Germany is set out in the accompanying set of claims marked as being for Germany. The subject matter to be protected for France and UK is set out in the accompanying set of claims marked as being for France and UK. Brief Description of the Drawing The sole figure illustrates a detailed schematic diagram of a reverse battery protection circuit for protecting an integrated circuit in accordance with the present invention. Detailed Description of the Drawing Referring to the sole figure, there is illustrated reverse battery protection circuit 10 fabricated within integrated circuit (IC) 26 and being coupled between battery 12 and terminal 22. It is understood that terminal 22 is further coupled to additional circuitry wherein this additional circuitry is desired to be protected from reverse battery hook up. IC 26 includes protection circuit 10 as well as charge pump 18, and any additional circuitry (not shown) coupled to terminal 22. Terminal 24 is coupled to a ground reference of IC 26. Protection circuit 10 includes pass transistor 14 having a source electrode coupled to terminal 16 while the gate electrode of transistor 14 is coupled through resistor 42 to charge pump 18. The back gate of transistor 14 is coupled to the source electrode of transistor 14 while the drain electrode of transistor 14 is coupled to terminal 22. Protection circuit 10 further includes transistor/zener diode 30 having a base coupled to terminal 16 and an emitter coupled to the gate electrode of transistor 14 and to the drain electrode of transistor 32. The collector of transistor 30 is coupled to the collectors of transistor/zener diode 34 and transistor/diode 36 wherein the collector of transistor 36 is coupled to its base. The emitter of transistor 36 and the base of transistor 34 are both coupled to terminal 16. Moreover, the source electrode of transistor 32 and the back gate electrode of transistor 32 are coupled to terminal 16. The emitter of transistor 34 is coupled to the gate electrode of transistor 32 and returned to ground through resistor 38. The collector of transistor 34 is coupled to the collector of transistor/diode 40 wherein transistor 40 has its base coupled to its collector. The emitter of transistor 40 is coupled through resistor 42 to the gate electrode of transistor 14. Moreover, the emitter of transistor 40 is coupled to charge pump 18. Charge pump 18 is coupled through a diode and returned to ground reference. In normal operation, transistor 14 requires the use of charge pump 18 to generate a voltage of at least 5 volts above a voltage supplied by battery 12. Moreover, charge pump 18 is typically available on IC 26 since it is required for other applications. Under proper connection, the positive terminal of battery 12 is coupled to terminal 16 while the negative terminal of battery 12 is coupled to terminal 24. As a result, a positive supply voltage is applied to the source electrodes of transistors 32 and 14 as is desired. In this situation, transistor 14 is rendered operative while transistor 32 is rendered non-operative. As a result, the voltage appearing at terminal 22 (with respect to ground reference) will be substantially equal to the voltage appearing at terminal 16 (with respect to ground reference) less any IR drop occurring across transistor 14. However, if battery 12 is improperly hooked up in a reverse manner wherein the positive terminal of battery 12 is coupled to terminal 24 while the negative terminal of battery 12 is coupled to terminal 16 as represented by dotted lines 50 and 52. This now means that a negative voltage (with respect to ground reference) is applied to the source electrodes of transistors 14 and 32 as is not desired. Under this condition, transistor 32 is rendered operative thereby shorting the gate electrode of transistor 14 to its source electrode and, thus, rendering transistor 14 non-operative. As a result, the voltage appearing at terminal 16 is not passed to terminal 22 and thus is not supplied to any additional internal IC circuitry. Further, any epitaxial layers typically coupled to terminal 22 cannot conduct current and damage integrated circuit 26. Transistor 30 functions as a zener diode to protect excessive voltage from appearing on the gate electrode of transistor 14. Essentially, the base of transistor 30 is the anode of the zener diode while the emitter of transistor 30 is the cathode of the zener diode. Moreover, the collector of transistor 30 is the third terminal of the zener diode and is coupled to the collector of transistor 34 which is the epitaxial island. Similarly, transistor 34 functions as a zener diode to prevent excessive voltage from appearing on the gate electrode of transistor 32 wherein the base and emitters of transistor 34 respectively act as the anode and cathode of the zener diode while the collector of transistor 34 is coupled to the epitaxial island. Moreover, resistor 38 functions to provide charge to render transistor 32 operative under a reverse battery condition. Also, resistor 42 functions to decouple the gate electrode of transistor 14 from charge pump 18. It should be noted that components 30, 34, 32 and 38 are all fabricated in one epitaxial region which is biased by PNP transistors 36 and 40. The present invention assures that no epitaxial islands are tied to terminal 16. As a result, if the connections of battery 12 are reversed, there are not epitaxial islands to be forward biased. The present invention has several advantages. First, protection circuit 10 does not provide any additional DC loading on charge pump 18 when it is desired to enhance and turn on TMOS transistor 14. Second, under reverse battery conditions, charge pump 18 does not have to be heavily resistive or open for proper operation as is the case for prior art circuits. Thus, charge pump 18 does not have any special design requirements. Third, protection circuit 10 provides reverse battery protection without sacrificing power supply head room for low voltage operation since no series diodes are used. Moreover, the present invention quickly renders transistor 14 non-operative under a reverse battery condition. In particular, the discharge time constant for the gate electrode of transistor 14 is a product of the drain-source on resistance (R DSON ) of transistor 32 and the input capacitance (C ISS ) of transistor 14 which is substantially less than the turn off time for a passive gate termination scheme. By now it should be apparent from the foregoing discussion that a novel protection circuit for protecting internal circuitry of an integrated circuit from a reverse battery connection has been provided. The protection circuit includes a pass transistor which is rendered operative when the supply voltage is properly connected to the integrated circuit. However, when the power supply is improperly connected, a second transistor becomes active thereby rendering the pass transistor inactive and not allowing the reverse supply voltage to be applied to the internal circuitry. While the invention has been described in specific embodiments thereof, it is evident that many alterations, modifications and variations will be apparent to those skilled in the art.

Claims: Claims for the following Contracting State : DE A circuit (10) for protecting internal circuitry of an integrated circuit (26) from reverse battery connection, the integrated circuit (26) including a charge pump (18) and first (16) and second (24) terminals, the circuit (10) comprising: first means (14) coupled between the first terminal (16) and the internal circuitry for passing a voltage appearing across the first(16) and second (24) terminals to the internal circuitry when the integrated circuit (26) is properly connected to a battery (12), said first means (14) having a first current carrying electrode and a control electrode receiving a voltage generated by the charge pump (18); second means (32) for rendering said first means (14) non-operative by shorting the first current carrying electrode of the first means (14) to the control electrode of the first means (14) when the integrated circuit (26) is improperly connected to the battery (12), thereby blocking said voltage appearing across said first (16) and second (24) terminals from being passed to the internal circuitry, said second means including a first transistor (32) having first and second current carrying electrodes and a first resistor (38) coupled between a control electrode of said first transistor (32) and the second terminal (24), said first current carrying electrode of said first transistor (32) coupled to the control electrode of said first means (14), said second current carrying electrode of said first transistor (32) coupled to the first terminal (16), wherein said first transistor (32) is rendered operative when the integrated circuit (26) is improperly connected to the battery (12); first zener diode means (34) coupled across said second current carrying and said control electrodes of said first transistor (32) for limiting a voltage appearing thereacross; bias means (36, 40) coupled to the first terminal (16) and the charge pump (18) for biasing an epitaxial region in which said first transistor (32), said first zener diode means (34) and said first resistor (38) are fabricated. The circuit (10) according to claim 1 wherein said second means further includes second zener diode means (30) coupled across said first current carrying electrode and said control electrode of said first means (14) for limiting a voltage appearing thereacross, said second zener diode means (30) also being fabricated in said epitaxial region. The circuit (10) according to claim 2 wherein said first zener diode means comprises a second transistor (34) having a collector, a base and an emitter, said base of said second transistor (34) coupled to the first terminal (16), said emitter of said second transistor (34) coupled to said control electrode of said first transistor (32), wherein said second zener diode means comprises a third transistor (30) having a collector, a base and an emitter, said base of said third transistor (30) coupled to the first terminal (16), said emitter of said third transistor (30) coupled to said control electrode of said first means (14), said collector of said third transistor (30) coupled to said collector of said second transistor (34), wherein said bias means (36, 40) comprises: a fourth transistor (36) having a collector, a base and an emitter, said collector of said fourth transistor (36) coupled to said collector of said third transistor (30), said base of said fourth transistor (36) coupled to said collector of said fourth transistor (36), and said emitter of said fourth transistor (36) coupled to said first terminal (16); and a fifth transistor (40) having a collector, a base and an emitter, said collector of said fifth transistor (40) coupled to said collector of said fourth transistor (36), said base of said fifth transistor (40) coupled to said collector of said fifth transistor (40), said emitter of said fifth transistor (40) coupled to the charge pump (18); and wherein said second means further comprises a second resistor (42) coupled between said emitter of said fifth transistor (40) and the control electrode of said first means (14). A method for providing reverse battery protection to internal circuitry of an integrated circuit (26), the integrated circuit having first (16) and second (24) terminals for coupling to a battery (12), the method comprising the steps of: allowing a voltage appearing at the first terminal (16) to pass through a transistor (14) to the internal circuitry by providing a voltage generated by a charge pump (18) to a control electrode of said transistor (14) when the integrated circuit (26) is properly coupled to the battery (12); biasing an epitaxial region in which a further transistor (32) and a resistor (38) are fabricated; rendering the further transistor (32) operative using the resistor (38) when the integrated circuit (26) is improperly coupled to the battery (12); actively disabling said transistor (14) when the integrated circuit (26) is improperly coupled to the battery (12) thereby preventing said voltage appearing at the first terminal (16) to pass to the internal circuitry, wherein the further transistor (32) substantially shorts a control electrode of the transistor (14) to a current carrying electrode of the transistor (14) when the further transistor (32) becomes operative and the charge pump (18) is decoupled from the transistor (14). Claims for the following Contracting States : FR, GB A circuit (10) for protecting internal circuitry of an integrated circuit (26) from reverse battery connection, the integrated circuit (26) including first (16) and second (24) terminals, the circuit (10) comprising: first means (14) coupled between the first terminal (16) and the internal circuitry for passing a voltage appearing across the first (16) and second (24) terminals to the internal circuitry when the integrated circuit (26) is properly connected to a battery (12), said first means (14) having a first current carrying electrode and a control electrode receiving a voltage generated by a charge pump (18), the circuit characterised by : second means for rendering said first means (14) non-operative by shorting the first current carrying electrode of the first means (14) to the control electrode of the first means (14) when the integrated circuit (26) is improperly connected to the battery (12), thereby blocking said voltage appearing across said first (16) and second (24) terminals from being passed to the internal circuitry, said second means including a first transistor (32) which is rendered operative when the integrated circuit (26) is improperly connected to the battery (12). The circuit (10) according to claim 1 wherein said second means includes: the first transistor (32) having first and second current carrying electrodes and the control electrode, said first current carrying electrode of said first transistor (32) coupled to said first means (14), said second current carrying electrode of said first transistor (32) coupled to the first terminal (16); first zener diode means (34) coupled across said second and control electrodes of said first transistor (32) for limiting a voltage appearing thereacross; and bias means (36, 40) coupled to the first terminal (16) and the charge pump (18) for biasing an epitaxial region in which said first transistor (32) and said first zener diode means (34) are fabricated. The circuit (10) according to claim 2 wherein said second means further includes second zener diode means (30) coupled across said first means (14) for limiting a voltage appearing thereacross, said second zener diode means (30) also being fabricated in said epitaxial region. The circuit (10) according to claim 3 wherein said first zener diode means comprises a second transistor (34) having a collector, a base and an emitter, said base of said second transistor (34) coupled to the first terminal (16), said emitter of said second transistor (34) coupled to said control electrode of said first transistor (32), wherein said second zener diode means comprises a third transistor (30) having a collector, a base and an emitter, said base of said third transistor (30) coupled to the first terminal (16), said emitter of said third transistor (30) coupled to said control electrode of said first means (14), said collector of said third transistor (30) coupled to said collector of said second transistor (34), wherein said bias means (36, 40) comprises: a fourth transistor (36) having a collector, a base and an emitter, said collector of said fourth transistor (36) coupled to said collector of said third transistor (30), said base of said fourth transistor (36) coupled to said collector of said fourth transistor (36), and said emitter of said fourth transistor (36) coupled to said first terminal (16); and a fifth transistor (40) having a collector, a base and an emitter, said collector of said fifth transistor (40) coupled to said collector of said fourth transistor (36), said base of said fifth transistor (40) coupled to said collector of said fifth transistor (40), said emitter of said fifth transistor (40) coupled to the charge pump (18); and wherein said second means further comprises: a first resistor (38) coupled between the control electrode of said first transistor (32) and the second terminal (24); and a second resistor (42) coupled between said emitter of said fifth transistor (40) and the control electrode of said first means (14). A method for providing reverse battery protection to internal circuitry of an integrated circuit (26), the integrated circuit having first (16) and second (24) terminals for coupling to a battery (12), comprising the step of allowing a voltage appearing at the first terminal (16) to pass through a transistor (14) to the internal circuitry by providing a voltage generated by a charge pump (18) to a control electrode of said transistor (14) when the integrated circuit is properly coupled to the battery (12), the method being characterised by the steps of: rendering a further transistor (32) operative using a resistor (38) when the integrated circuit (26) is improperly coupled to the battery (12); actively disabling said transistor (14) when the integrated circuit (26) is improperly coupled to the battery (12) thereby preventing said voltage appearing at the first terminal (16) to pass to the internal circuitry, wherein the further transistor (32) substantially shorts a control electrode of the transistor (14) to a current carrying electrode of the transistor (14) when the further transistor (32) becomes operative and the charge pump (18) is decoupled from the transistor (14).

Inventors: HECK KARL R, HECK, KARL R.
Applicants: MOTOROLA INC, MOTOROLA, INC.
Application year: 1994
Main classification: H02H11
IPC codes: H02J7, H02H7, H02H11